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Air quality in Missouri

EPA monitors report from 20 of Missouri’s 115 counties. That is the honest limit of this page: the other 95 are not measured, not clean. In 2025 the most affected monitored county was St. Louis city, with 8 days above the moderate category.

20
Counties with monitors
95
Counties without
45
Days above moderate, 2025
Summed across monitored counties
10.6%
Adults with asthma
Population-weighted county estimate

County by county

Monitored Missouri counties

GoodModerateUnhealthy for sensitive groupsUnhealthyVery unhealthyHazardous
County90th %ile AQIAbove moderateMax AQI2025 days by category
St. Louis city778738
Clay County647156
Greene County624160
Jefferson County604150
St. Charles County714164
Clinton County673122
Jackson County633293
Lincoln County583122
Buchanan County622256
Jasper County582162
Ste. Genevieve County502108
Cass County551123
Cedar County551106
Perry County541105
Andrew County58093
Boone County49087
Callaway County51077
Monroe County47097
Stoddard County40043
Taney County52079

EPA Air Quality System annual summaries by county, 2025. The 90th percentile AQI describes a day worse than nine out of ten, which is a steadier measure than the annual maximum a single wildfire can set.

Not measured

95 counties without a monitor

No EPA monitor reported from these counties, so there is no air quality record to publish. Their radon zone is known, and radon is measured in the building rather than the air outside it.

Other states

Air quality elsewhere